Method of producing nodular iron



United States Patent 1. 2,980,530 METHOD OF PRODUCING NODULAR IRON Lester C. Crome, West Alexandria, Ohio, assignor to The Dayton Malleable Iron Company, Dayton, Ohio, a corporation of Ohio No Drawing. Filed Dec. 11, 1958, Ser. No. 779,544

'16 Claims. (Cl. 75-130) This invention relates to the production of gray iron castings having in the as-cast state graphitic carbon present therein in substantially nodular form, and more particularly to a process for producing such castings by the addition of a rare earth fluoride and a reducing agent therefor to the molten gray iron before pouring. This application is a continuation-in-part of my copending applications Serial No. 640,624, filed February 18, 1957, and Serial No. 641,870, filed February 25, 1957, now both abandoned.

Various methods are now known for producing from a gray iron mix a cast iron having, in the as-cast state and without subsequent treatment, all or a substantial part of the graphitic carbon present in the casting in socalled nodular" form. Such iron is now conventionally known as nodular iron and as having a nodular rnicrostructure with reference to the form in which the free or graphitic carbon is present in the finished casting. The term nodular is now conventionally understood to include truly spherulitic carbon nodules as well as other agglomerations of graphitic carbon which, while not being true spherulitcs, are still quite different from the flake form of graphitic carbon usually found in gray iron castings which are not nodular. As is well-known, cast iron having a nodular rnicrostructure possesses mechanical properties such as tensile strength, ductility, etc., substantially greater than a cast iron not having nodular rnicrostructure even though produced from a molten mix having substantially equivalent composition.

Most, if not all, of the various methods known today for producing nodular iron comprise adding a minor proportion of a nodularizing agent to the molten mix shortly before pouring or casting the mix. Among the many such additive materials or, as herein referred to, nodularizing agents described in the literature and known to men skilled in this art, perhaps the most widely used are magnesium, misch metal, certain calcium compounds, and various mixtures, alloys, and combinations thereof.

As will be understood, many of these nodularizing agents include materials having a fairly high cost, and it is desirable that the amount of nodularizing agent added be kept as low as possible consistent with obtaining the desired mechanical properties in the finished casting in order to keep the cost of producing the castings as low as possible. Furthermore, the presence of sulphur in the molten iron mix in proportions conventionally obtained when the mix is originally melted in a cupola has been found to be somewhat inimical to the nodularizing action of some if not all nodularizing agents. Also, melting the iron mix in the well-known direct arc type of foundry apparatus may be found to produce a molten mix which is not particularly susceptible to nodularizing, perhaps as a result of the arc melting process on nitrogen in the atmosphere.

It is now well known that certain rare earth metals have the effect of controlling the precipitation of graphitic carbon in a gray iron mix into a so-called nodular or'spherulitic form during cooling of the mix in a mold to produce a gray iron casting having the graphitic carbon therein in nodular or spherulitic form' in the casting as cast and without further treatment. The characteristics of rare earth metals, however, are such that, as it is attempted to. add themetals. directin :a ladlev...of molten.

iron prior to pouring, only a portion of the added metal "ice is dissolved in the molten iron and remains effective during the-cooling of the casting to produce the desired nodular rnicrostructure. A substantial part of the added metal is lost, as far as its nodular inducing function is concerned, by oxidation or combining with other elements present in the mix.

Since the cost of the added nodular inducing agent may be a significant or substantial factor in the cost of producing nodular iron, it is desired to add the nodular inducing agent to the molten iron in such a way that a maximum amount of the added material will be effective for nodular rnicrostructure formation.

According to this invention, it may be desired to have a preliminary treatment of the molten melt for increasing the susceptibility or responsiveness thereof to a nodularizing agent later to be added thereto, and such pretreatment is provided by treating the molten iron with a calcium slag reducing material prior to the addition of a nodularizing agent to the melt. As a further feature of this invention, a nodular inducing agent or nodularizing agent, such as one or more rare earth metals, is added to the molten iron in the form of a compound, preferably the fluoride, and a reducing agent for such fluoride, such as calcium silicide or calcium carbide, is also added to reduce the fluoride in situ in the molten mix for liberating the rare earth metal nodularizing agent for direct solution or incorporation into the molten iron with substantially less loss of the nodularizing agent by oxidation or combination with other elements as would be the case if the nodularizing agent were added to the molten mix originally in elemental or free metallic form.

One object of this invention is to provide a slag treatment for increasing the susceptibility of a molten iron mix to the nodularizing action of a nodularizing agent.

Another object of this invention is to provide a pretreatment slag composition for use in the production of nodular iron as a preliminary treatment to increase the susceptibility of a molten iron mix to nodularizing by a nodularizing agent.

A further object of this invention is to provide a process of the character described for producing iron castings having in the as-cast state a nodular microstructure by the addition to a molten gray iron mix of rare earth fluorides and a reducing agent therefor.

vAnother object of this invention is to provide a method of inducing rare earth metals into a molten iron mix for inducing therein a nodular rnicrostructure on the molten iron.

A further object of this invention is to provide a combined additive or addition agent of a molten iron mix to produce upon reaction therein a nodular inducing agent eflective to control precipitation of graphitic carbon in said mix into a nodular form.

Still another object of this invention is to provide a method for reducing rare earth fluorides in a molten iron mix for liberating in said mix rare earth nodular inducing metals for direct solution therein to control precipitation of graphitic carbon into a substantially nodular form.

Other objects and advantages of this invention will be apparent from the following description and the app-ended claims.

Satisfactory results have been obtained according to this invention by utilizing a slag made up of one or more calcium mineral materials and carbon with or withoutthe addition of a fluxing material thereto. Among the calcium materials satisfactory for practicing this invention are included limestone, calcium silicide, calcium oxide, calcium carbide, calcium'fluoride, and mixtures thereof, although practicing of this invention is not limited to these particular materials. As will be understood, however, there are a number of calcium materials which produce the desired characteristics in the melt but, for

other reasons, are not preferred. For example, calcium chloride apparently provides the desired metallurgical properties but, because of its deliqnescent character, it is diflicultto' handle in that any moisture in the slag causes undesired if not dangerous'eifects during the addition thereof to the molten iron, and the sulphate and nitrate are not preferred because of the presence of sulphur and nitrogen therein.

The carbon can be added in a variety of forms such as coke, graphite, or calcium carbide, and a preferred fiuxing material is calcium fluoride or'fluorspar.

A preferred slag embodying and for practicing this invention comprises a combination of a calciumcarbonate as limestone, calcium fluoride as fluo rspar, and coke, and preferred proportions for these materials (by weight on thefmolten mix) are 3% limestone, fluorspar and 1% fcok'e.

The'calcium slag' materials of this invention are-added totliemolten iron mix after melting'and ashort time before the, addition thereto of a nodularizing agent; If theinodularizing agent is added to the iron melt in a ladle upon tapping the melt from the furnace and before casting the melt from the ladle into molds-satisfactory results are obtained by addiugthe calcium slag on top of the melt in, the furnace and before tapping into the ladle. The slag is allowed to stay on the melt for a short time ofthe order of to minutes and the thus treated mixis tapped from the furnace into a ladle. It will be understood that the slag treatment according to this inventionis appropriate for use with various gray iron mixes having various compositions susceptible ofnodularizing as is now well understood in this art.

Whereasthe mechanics of the effect produced by a calcium slag treatment embodying this invention are not known'completely, it has been noted that such treatment has a pronounced influence on the susceptibility of the molten iron to the nodularizing action of a. nodularizing agent. The effect appears to be more than merely desulphurizing, and it is believed to include a reducing efiect resulting from the carbon present in the slag or oxygen in the molten mix which would otherwise react undesirably with the nodularizing agent. It is not believed, however, that this enhanced susceptibility is achieved by actual solution of the calcium slag in the molten mix to become an additional component thereof during pouring because the enhanced characteristics are obtained although very little if any of the calcium mate 'rial is discernibly retained in the finished casting. That is; the enhanced results of this invention are obtained even'when as little as less than .005 calcium is retained in the finished casting.

The calcium slag p-retreatmentof this invention should also be distinguished from the known use of certain calcium materials as nodularizing agents suchas, for example, those referred to in Patent No. 2,662,820, This distinction becomes apparent when it is noted that the calcium slag treatment according to this invention, even whencalcium silicide and calcium fluoride are included in the slag, does not occur under such conditions as would produce a nodular iron in the absence of an additional nodularizing'agent. It also'appears that the slag treatment has an influence on the properties of the molten mix by' some mechanism other than the actual solution of the calcium or other materials in the mix. It'has been noted, however, that the utilization of calcium fluoride as a fluxing material somewhat enhances the eifect of calcium slags embodying this invention.

As perhaps suggestive of an explanation of the possible reactions involved, the following equations are noted:

CaCOpCaO-i-CO;

4 III 2CaO+CaC 23Ca+2CO It will be noted that the last -two reactionsindicated above are reversible, and this also suggests that the mechanism? of the slag treatment according to this inven tion is of the solution of, the calcium in the molten iron, perhapsonly momeritarily afterwhich the calcium again comes out of solution, because, for example, of theabove notedminuteproportions of, calcium retainedin the castmg. I

As illustrative of the results achieved according to this invention ainumber of substantially equivalent gray ironmixes-were. melted, giving a slag pretreatment and then nodularized and. cast. These melts were made from a mixture of;% of iapig ironcontaining approximately 088% silicon, 0.028% sulphur, 0.028% phosphorous, 0.26% manganese, and above 4% carbon; to which was added about 20% of silvery iron containing approximately 10% silicon." In each case the nodularizing agent was 0.8% oft an alloy of'5% miscir metal, 20% magnesium and 75% copper. For each run a sand casting wasmade in the form of a .so-called keel b1ock'with two coupons, one; of which was immediately tested for ultimate tensile strength and elongation, While, the other,was;maintained-at about 1300 F. for about 8; hours before being tested.

The results ofi-these illustrative runsindicate that satisfactory nodularization and enhanced physical properties were achieved with, the molten mixes which had received the-calcium slag pretreatrnentaccording to this invention by they-addition of only: 0.8% of the additive nodularizing alloy, whereaslasmuch as 11.25% of the same alloy is necessary to give'iequivalent nodularizing-results in such moltenmixes whichv are not subjected first to the calcium slag pretreatn ient. Since the additive alloy is comparatively expensive; anda substantial factor in the cost of production of nodular iron castings, this sharp reduction in the amount oflalloy needed, achieved by the pretreatment. according to; this invention, is a substantial commercial factor in theproduction of nodular iron castings.

The following table setsforth the resultsin a number of theseillustrative runs, showing the composition of the slag; th e amount; of time between the addition of slag and tapping; of themix into theladle for the addition thereto of thenodularizingagent, as well as the results of the mechanicalprop ertytests on the casting immediately broken from thempldfind that which were held at 1300?. F. forabout; .8 hours before being tested:

AS Cast Held8hrs. Slag Time Ultimate Elong. Ultimate Elong.

20 95, 100 3. 0 es, 200 a. 5

20 as, 000 Y 3.5 74,100 14.5

It will thus be apparent that a pretreatment and calcium slag compositions are provided according to this invention which substantially enhance the susceptibility of a molten gray iron mix to the eifect therein of a nodularizing agent, and that the relatively inexpensive materials of the slags provide a substantial saving in the amount of costlier nodularizing agents which are used as well as being readily and conveniently added in the furnace prior to tapping the melt.

When the rare earth metals, such as cerium, misch metal, didymium, and other such metals or mixtures of metals, are added to a molten gray iron mix to exercise their well-known function of controlling the precipitation of graphitic 'carbon therein into a nodular or spherulitic form, a substantial amount of the added metal is lost during or shortly after the addition as by oxidation, preferential combination with sulphur, and other causes, all of which remove or subvert some of the added metal and prevent or interfere with the nodular inducing function thereof. It has been discovered, however, that, according to this invention, the rare earth metals may be added to a molten iron mix in the form of a compound which will prevent or minimize loss of the metal during addition. After addition to the mix, then, this compound can be reduced by the action of an added reducing agent to yield the rare earth metal itself for direct solution into the molten iron.

As will be understood, of course, a number of possible reactions may occur when a rare earth metal and/or a compound thereof is added to a molten iron mix at elevated temperatures, and, when rare earth compounds are added to molten iron mixes, the resulting reactions will depend in large measure on such thermodynamic consideration as heats'of formation and free energies of the various reacting compounds. As based on such considerations, rare earth compounds and reducing agents can in the mix. In such an environment the reaction involved 7 will preferentially approach as an end point the production of that one of the several possible resultant compounds which has the highest heat of formation and the lowest free energy. Since the rare earth fluorides have lower heats of formation than calcium fluoride, the desired reduction takes place.

- Accordingly, in a situation where calcium has an opportunity to reduce cerium fluoride, the energy conditions such as the relative heats of formation will encourage the replacement of cerium by calcium, thereby reducing cerium fluoride to the metallic state as desired.

With the foregoing considerations in mind, it will be noted that the fluorides of the various rare earth metals and mixtures thereof all have heats of formation of an order of magnitude with respect to calcium fluoride so that any of the rare earth fluorides and mixtures thereof will-be reduced by or replaced by calcium to liberate the metal when reacted in a molten iron mix.

- According to this invention, then, rare earth metals in the form of the fluorides are added to a-molten iron mix for reduction therein by a reducing agent containing calcium. Calcium silicide is preferred as a reducing agent and better results are obtained with calcium silicidethan with other, calcium materials. Also calcium itself has nodularizing properties, and some of the calcium may have its own effect in the iron during the course of the reducing reaction. Commercial grade calcium silicide usually contains approximately 30% calcium and 60% silicon, and this commercial grade of calcium silicide has been found satisfactory. It is such a material that is to be understood in the following examples when calcium silicide is mentioned.

Although many metallic elements are now known to have a nodular inducing effect when added to molten iron, the rare earth elements for the process ofthis invention have been found most satisfactory. They may be used individually as fluoride or, as preferred from a practical standpoint, as mixtures of fluorides. Of the various rare earth materials, misch metal is most readily available. As is well known, misch metal contains approximately 45% to 50% cerium with substantial proportions of lanthanum, praseodymium, neodyrninum, and minor proportions of other rare earths. Both misch metal in metallic form and a mixture of rare earth fluorides (hereinafter sometimes referred to as misch metal fluorides) are available commercially. The fluorides may be produced from monazite ore which contains some or all of about 14 rare earth metals. In processing the ore, which is principally a source of thorium, the various rare earth elements are readily converted to sulfates and thence to fluorides in known manner.

In addition to some possible assistance in nodular formationachieved by using calcium in the reducing agent, the calcium is also preferred by virtue of its position with respect to cerium in the chemical activity series and as a further driving force, along with other considerations as the heats of formation, to urge the desired reducing reaction preferentially; to completion or other possible reactions which might occur with the same reactants. Thus, calcium is above cerium in the activity series and separated therefrom by beryllium, thorium, magnesium, barium, strontium, and aluminum. In considering these other materials above cerium as possible components of the reducing agent, it is noted that beryllium is not satisfactory because of the almost inevitable formation of the very toxic beryllium oxide at the temperatures encountered with a molten iron mix. As a practical matter thorium is not preferred because of its presently limited availability for uses other than those connected with atomic energy developments as well as because of its greater usefulness for other purposes.

Magnesium is a well-known nodular inducing agent in its own right, and it would appear practically and commercially pointless to attempt to use it here as a reducing agent. Although barium and strontium are operative with this invention, the cost and lack of commercial availability of appropriate compounds thereof indicate that these'elements are not preferred, and aluminum, perhaps because of its being so close to cerium in the activity series, does not give practically satisfactory results.

Satisfactory results have been achieved according to this invention using various combinations of proportions of calcium silicide and misch metal fluoride. From the standpoint of etficiency and practical yield of nodular inducing agent, the proportions of from 2 to 4 parts of calcium silicide to 1 part of rare earth fluoride are preferred, and satisfactory results have been achieved by adding from 0.5% to 3%, and preferably 1% .to 2%, of such a mixture of calcium silicide and rare earth fluorides to the ladle of molten iron.

As illustrative of a process embodying this invention, the following examples are noted:

was melted with an additional 0.50% silicon. To the molten mix in the ladle before pouring was added 1.25% of a mixture of 4 parts calcium silicide to 1 part misch metal fluoride. Casting in the form ofthe well-known fkeel bIock Were east ina sand mold. One was shaken out of-jthe mold when solidified" and tested for-its various physical; properties. This'casting 1 showed: a 'Brinellnum ber of'z235; tensile stren'g'thof 95,700 pounds and an Example 11 A pig iron charge analyzing- Percent Carbon 4.46 Silicon 1.96 Sulphur 0.021 Phosphorus 0.023 Manganese 0.17

was melted with an additional 1% silicon. To the melted charge in the ladle was added 4% of a mixture of 2 parts calcium carbide and 1 part misch metal fluoride, and the melt was cast in a sand mold. The resultant casting, upon testing, had a Brinell number of 179, tensile strength of 70,300 pounds'and an elongation of 8%.

A further commercial scale run embodying this" invention is also noted:

Example 111 A 9,000 pound charge of pig iron analyzing Percent Carbon 4,34 Silicon 1.91 Sulphur 0.024 Phosphorus 0.026 Manganese 0.17

was melted and heated to approximately 2800 F; at which time 1.2% additional silicon was added from 75% fer'rosilicon. A slag of 2% lime, 0.75% fluorspar, and

1%. petroleum coke was then added to the furnace and held for 20 minutes, after which 2000 pounds of the mix was tapped into a ladle and 1% of a mixture of 4 parts calcium silicide to 1 part misch metal fluoride-was added. A 1" .keelbl'ockicasffrom this ladle tested to have a Brinell number of 174, ultimate tensile strength of 71,700 pounds and anelongation of 20%.

It :should be noted, as will be understood-by men skilled in. the' art, that for castings" in which a predominately pearlitic structure is desired, tensile strengths ofin' excessi of 80,000 pounds'and elongationsof inexcess of 2% are achieved according to this invention, while, with castings in which a predominately ferritic structure is produced, tensile strengths of in "excess of 60,000 pounds with elongations of 10%' or more-are achieved.

It'should also be noted that the various methods heretofore devised for extending'the effective time of rare earth type nodular inducing agents in a molten mix and methods heretofore devised for otherwise enhancing the yield or effectiveness of such agents are applicable to methods embodying this invention, since the function of inducing graphite precipitation into a nodular form is achieved with this invention by the rare earth metals liberated in the molten mix from the reduction of the added compound, and the mechanism of such graphite precipitation is believed to be substantially the same as if the elemental metalwere added as such to the molten mix instead of being producedtherein-by retluctiono'fa compound of thernetal. V

As mentioned above, howeven the useiof a calcium ompound" as the reducing agenr probably contributes its own part in .the -nodularmic'rostructure formation as disclosed-for example,':inEPatent No. 2,662,820.. Generally.

substantially the same: considerations as to" the length of time before 'pouring's-duringr which. the 'no-dular'. reducing:

agent will 'remain' effective 5 in the moltenmetal 1 are ob tained with processes obtaining this". invention as with other nodular iron;processes in which rare earth metals are added: as such to the molten mix.'

Also, in view of the nodularizing. effect of calcium. or calciumisilicide, it will be apparent that, as the proport-ion of fluoridein the addedmixture is decreased. the proportion of calcium silicide must beincreased to obtain the desired completeness of nodularization'fromthe-additive. Since in many instances it may not be desired so to increase the calcium silicideaddition because, for-exainple, of the other effects-Which additionsof-this material produce in molteniron; Thepreferredrang'esare as set forthabovei.'e., 2*to 4" parts of calcium'silicide for each part of rare earth fluoride. These proportions may be varied, however, withinwide-ranges-and consid'-- ering that, for the reduction 'reaction to beweflicient; a suflicient excess ofthe reducing agent' must be presentg and alternatively, suflicient fluorideshould be usedto achieve no'dularizing without-having to addan undesirablyhigh amount of-calcium silicide. That is, there appears to be a definitely cooperative and synergistic interaction between the fluoride and calcium additives: The reactions may be considered as first having": the fluoride-flux the calcium material in the solution where some of'it then reduces the'fiuoride to provide rare earth metals for nodularizing whileother ofthecalcium mate rial may have its own nodulariz'ing effect after being fluxed in the'solution by the fluoride;

Although," as will be understood, itis' quite possible to obtain nodular microstructures in castings in'--accordance with thisinvention and utilizing various types ofiron mixes wthout sucha preliminaryacalcium slag-pretreatment, in commercial operations more satisfactory results are achieved by the pretre'atme'nt of the iron mix, in accordance with said copendi'ng applications prior to'the' addition of the nodular'izing agent material's 'in accordance with this invention, andsuch more satisfactory'rsults are mostemphatically demonstrated in' lconnection with' the fact that th'e'p'retreatm'ent steps appear to provide additional assurance that the desired nodular microstructure and enhanced physical properties will beroutinely obtained time" after time with all the-castings poured from a particular meltor' -a particular 1adleand without the commercially or economically undesirable question orpossibility-that, iri som'e c'a'ses, a few castings from oneheat or one pouring may; for reasons ofvaria' tions in the melt during pouring, etc-z, 'fail 'to achieve the desired nodular microstructure- While the methods, compositions and products described herein constitute preferred embodiments'- of the invention, it'is to be understood that the invention is not limited to-these precise methods, compositions and prod nets, and that changes m'ay-be made 'th'erein without departing from the scope of-the'invention which is defined in the appended claims.

What is claimed is:

1. In the production of' as-castnod'ular iron'from'a moltengray iron mix by the use of rare earth-metals'as the nodularizing agent added to said molten mix, the method of increasing the efficiency of incorporation of said agent into said mix'andof-decreasing the amount of said agent added'to said mix and the amount of said agent lost duringsaid addition which comprises the steps of preparing a molten gray iron mixytreating said mix with a slag material comprising calcium carbonate and a carbonaceous'materialand calciumfluoride for-enhancing the responsiveness-of said mix 'tdthe effect of-said nodularizing agent, thereafter adding to said mix blfo're casting a rare earth metal fluoride andar-redudngagem therefor, efiectingreduction of-said rare 'earth nietal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting.

2. In the production of as-cast nodular iron from a molten gray iron mix by the use of rare earth metals as the nodularizing agent added to said molten mix, the method of increasing the efficiency of incorporation of said agent into said mix and of decreasing the amount of said agent added to said mix and the amount of said agent lost during said addition which comprises the steps of preparing a molten gray iron mix, treating said mix with a slag material comprising calcium carbonate and a carbonaceous material for enhancing the responsiveness' of said mix to the elfect of said nodularizing agent, thereafter adding to said mix before casting a rare earth metal fluoride and a calcium reducing agent therefor, effecting reduction of said rare earth metal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting.

, 3. In the production of as-cast nodular iron from a molten gray iron mix by the use of rare earth metals as the nodularizing agent added to said molten mix, the method of increasing the efliciency of incorporation of said agent into said mix and of decreasing the amount of said agent added to said mix and the amount of said agent lost during said addition which comprises the steps of preparing a molten gray iron mix, treating said mix with a slag material comprising calcium carbonate and a carbonaceous material for enhancing the responsiveness of said mix to the effect of said nodularizing agent, thereafter adding to said mix before casting a rare earth metal fluoride and calcium silicide as a reducing agent therefor, effecting reduction of said rare earth metal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting.

' 4. In the production of as-cast nodular iron from a molten gray iron mix by the use of rare earth metals as the nodularizing agent added to said molten mix, the method of increasing the efliciency of incorporation of said agent into said mix and of decreasing the amount of said agent added to said mix and the amount of said agent lost during said addition which comprises the steps of'preparing amolten gray iron mix, treating said mix with a slag material comprising calcium carbonate and a carbonaceous material for enhancing the responsiveness of said mix to the effect of said nodularizing agent, thereafter adding to said mix before casting a rare earth metal fluoride and calcium silicide as a reducing agent therefor in the proportions of 2-4 parts of silicide to 1 part of fluoride, effecting reduction of said rare earth metal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting.

5. In the production of as cast nodular iron from a molten gray iron mix by the use of rare earth metals as the nodularizing agent added to said molten mix, the method of increasing the efficiency of incorporation of said agent into said mix and of decreasing the amount of said agent added to said mix and the amount of said agent lost during said addition which comprises the steps of preparing a molten gray iron mix, treating said mix with a slag material comprising calcium carbonate and coke for enhancing the responsiveness of said mix to the effect of said nodularizing agent, thereafter adding to said mix before casting /z% to 3% of a mixture of a rare earth metal fluoride and calcium silicide as a reducing agent therefor, effecting reduction of said rare earth metal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting.

6. In the production of as-cast nodular iron from a molten gray iron mix by the use of rare earth metals as the nodularizing agent added to said molten mix, the method of increasing the efficiency of incorporation of said agent into said mix and of decreasing the amount of said agent added to said mix and the amount of said agent lost during said addition which comprises the steps of preparing a molten gray iron mix, treating said mix with a slag material comprising calcium carbonate and coke for enhancing the responsiveness of said mix to the effect of said nodularizing agent, thereafter adding to said mix before casting 1% to 2% of a mixture of a rare earth metal fluoride and calcium silicide as a reducing agent therefor, effecting reduction of said rare earth metal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting,

7. In the production of as-cast nodular iron from a molten gray iron mix by the use of rare earth metals as the nodularizing agent added to said molten mix, the method of increasing the efficiency of incorporation of said agent into said mix and of decreasing the amount of said agent added to said mix and the amount of said agent lost during said addition which comprises the steps of preparing a molten gray iron mix, treating said mix with a slag material comprising calcium carbonate and coke for enhancing the responsiveness of said mix to the effect of said nodularizing agent, thereafter adding to said mix before casting /z% to 3% of a mixture of a rare earth metal fluoride and calcium silicide as a reducing agent therefor in the proportions of 2-4 parts silicide to 1 part fluoride, effecting reduction of said rare earth metal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting.

8. In the production of as-cast nodular iron from a molten gray iron mix by the use of rare earth metals as the nodularizing agent added to said molten mix, the method of increasing the efficiency of incorporation of said agent into said mix and of decreasing the amount of said agent added to said mix and the amount of said agent lost during said addition which comprises the steps of preparing a molten gray iron mix, treating said mix with a slag material comprising calcium carbonate, coke and fluorspar for enhancing the responsiveness of said mix to the effect of said nodularizing agent, thereafter adding to said mix before casting 1% to 2% of a mixture of a rare earth metal fluoride and calcium silicide as a reducing agent therefor in the proportions of 2-4 parts silicied to 1 part fluoride, effecting reduction of said rare earth metal fluoride to said rare earth metal by said reducing agent in said molten mix for nodularizing action therein, and pouring the thus treated mix into a mold to form said casting.

9. In a method of the character described for producing nodular cast iron by a ladle addition of a nodularizing agent to a molten iron mix, the pre-treatment steps which comprise adding a slag including calcium carbonate and carbonaceous reducing material to said molten mix prior to ladle addition of said nodularizing agent, tapping said thus treated mix into a ladle after a predetermined short length of time effective for diffusion of said calcium slag through said mix, and then making said ladle addition of said nodularizing agent.

10. In a method of the character described for producing nodular cast iron by a ladle addition of a nodu1arizing agent to a molten iron mix, the pre-treatment steps which comprise adding a reducing slag including limestone and coke to said molten mix prior to ladle addition of said nodularizing agent for removal of sulphur and oxygen from said mix and otherwise enhancing the susceptibility thereof to said nodularizing agent, tapping said thus treated mix into a ladle after a predetermined 11 short length of time effective for diffusion of said slag through said mix, and then making said ladle addition of said nodularizing agent.

11. In a method of the character described for pro-' ducing cast iron having in the as-cast state graphitic carbon present in nodular form, the steps which comprlse forming a molten iron mix, adding to said mix before pouring a slag of limestone, carbon, and fluorspar, thereafter adding to said mix a nodularizing agent, and cast-.

ing'said thus treated mix.

12.In'a method of the character described for producing nodular cast iron by a ladle addition of a nodularizing agent to a molten iron mix, the pretreatment steps for increasing the responsiveness of said molten iron' mix' to said nodularizing agent which comprises adding tosaid molten iron mix prior to said ladle addition of said-nodularizing agent a slag comprising a mixture of carbonaceous material and a calcium carbonate material, ho1ding-said thus treated mix with said slag-added thereto for a predetermined short length of time effective for diffusion of said slag through said mix, and-then making said ladle addition of said nodularizing agent to said-thus treated mix prior to casting said mix;

13. In a method of the character described for producing-nodular cast iron by a ladle addition of a nodularizing agent to a molten iron mix, the pretreatment steps for-increasing the responsiveness of said molten iron mix to said nodularizing agent which comprise adding to said molten iron mix prior to said ladle addition of said nodularizing agent a slag comprising a mixture of limestone and coke, holding said thus treated mix with said slag added thereto for a predetermined short length of time eflective for diliusion of said slag through said mix, and then making said ladle addition of said nodularizing agent to said thus treated mix prior to casting said mix.

14. In a method of the character described for producing nodular cast iron by a ladle addition of a nodularizing agent to a molten iron mix, the pretreatment steps for increasing the responsiveness of said molten iron mix to said nodularizing agent which comprise adding to said molten iron mix prior to said ladle addition of said nodularizing agent a slag c mprising a mixture of limestone, fluorspar and coke, holding said thus treated mix with said slag added thereto for a predetermined short length ofi time effective for diffusion of-said; slag through saidimix; andnthen-making said ladleaddition-ofr said nodularizing agent-: to :said thus treated; mix prior: to-castingsaid mix. t

15; In amethod of .the character described for producinggnodularcast iron by a ladle additionof anodu larizing agent to a molten iron mix, ,the-pretreatment, steps 'for-increasing-tthe responsiveness of said molten; iron-mix 'to-said nodularizing agent which. compriseadding; to said molten ironrnix prior to said'ladle addition; of' said nodularizing agent a slag comprising amixture'r of 3% limestone; %%-fluorspar and 1%cokeby weight: on'said mix, holding said thus treated'mix WithLSaidslag; added thereto ,for a predetermined short lengthof time efiective forxdifiusion-ofsaid slagthrough said mix, and: then making said ladle addition of Esaidnodularizing: agent to said thus treatedimixpriortocasting'said mix.

16. In amethod of: the character described for produc-- ingsnodular cast iron bya-ladle addition of a nodularizing agent to a a molten ironnmix; the pretreatment steps: for increasing the responsiveness of said molten iron mix to said nodularizing agent which comprise adding to said molten iron mix prior to said ladle addition of said nodularizing agent a slag comprising a mixture of carbonaceous reducing material and: a calcium mineral compound selected from the group consisting of the carbonate, silicide, halide, oxide, and mixtures thereof, holdingsaid thus treated mix with said slag added there-- to for a predetermined short length of time effective for diffusion of said slag through said mix, and'then making said ladle addition of said nodularizing'agent to saidthus treated mix prior to casting said mix.

References Cited in the file of this patent UNITED STATES PATENTS 170,420 Warner Nov. 23. 1875 2,750,284 Ihrig June 12, 1956' 2,779,675 Vennerholm .Jan. 29, 1957 2,794,731 Keizo -Iwase et al. June 4, 1957- 2,821,473 Moore Jan. 28, 1958 2,865,735- Timmerbeilet al. Dec. 23, ,1958;

FOREIGN PATENTS 203,754 Australia v, Oct. 16, 1956 670,245 Great Britain Apr. 16,1952

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 2380 530 April 18 1961 Q Lester C, Crome It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent, should read as corrected below Column 6 line 75, for "Casting' read Castings column 7 line 22 in the table of Example 2 right-hand column. for "017" read 0013 --3 column 11 line 15, for "comprises" read comprise -O Signed and sealed this 19th day of September 1961 (SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC 

1. IN THE PRODUCTION OF AS-CAST NODULAR IRON FROM A MOLTEN GRAY IRON MIX BY THE USE OF RARE EARTH METALS AS THE NODULARIZING AGENT ADDED TO SAID MOLTEN MIX, THE METHOD OF INCREASING THE EFFICIENCY OF INCORPORATION OF SAID AGENT INTO SAID MIX AND OF DECREASING THE AMOUNT OF SAID AGENT ADDED TO SAID MIX AND THE AMOUNT OF SAID AGENT LOST DURING SAID ADDITION WHICH COMPRISES THE STEPS OF PREPARING A MOLTEN GRAY IRON MIX, TREATING SAID MIX WITH A SLAG MATERIAL COMPRISING CALCIUM CARBONATE AND A CARBONACEOUS MATERIAL AND CALCIUM FLUORIDE FOR ENHANCING THE RESPONSIVENESS OF SAID MIX TO THE EFFECT OF SAID NODULARIZING AGENT, THEREAFTER ADDING TO SAID MIX BEFORE CASTING A RARE EARTH METAL FLUORIDE AND A REDUCING AGENT THEREFOR, EFFECTING REDUCTION OF SAID RARE EARTH METAL FLUORIDE TO SAID RARE EARTH METAL BY SAID REDUCING AGENT IN SAID MOLTEN MIX FOR NODULARIZING ACTION THEREIN, AND POURING THE THUS TREATED MIX INTO A MOLD TO FORM SAID CASTING. 